The present invention relates to signal processing of format conversion of picture signal, particularly to a method and a circuit for signal processing of format conversion of picture signal preferable to converting a plurality of kinds of formats of picture signals into picture signals of predetermined display formats of picture output devices or conversion of flexible compression and flexible expansion of pictures in a horizontal and a vertical direction, or the like.
In recent years, with progress in multimedia, in respect of picture signals, kinds and modes of pictures to be handled increase rapidly and are advancing in a direction of diversification. Further, in respect of picture output devices for displaying pictures, other than CRT (Cathode Ray Tube), planar displays such as a liquid crystal display device, a plasma display panel and the like have frequently been used. Therefore, it is indispensable for information terminal devices in correspondence with multimedia to be provided with a function of receiving many kinds and many modes of picture sources and displaying them.
As representative methods for realizing the function, there are known a method of dealing with by display and a method of dealing with by signal processing. According to the former method, a picture is displayed by widely setting an operational range of a deflection system of a picture output device and performing a scanning operation in a mode in compliance with a signal format of input pictures, which has been reduced into practice as multi scan system. Although this is an effective method which can be realized at a comparatively low cost when a display unit is a CRT, it is difficult to apply in a planar display such as a liquid crystal display device, a plasma display panel or the like having a constant number of display picture elements.
According to the latter method, format conversion is performed by signal processing and pictures are displayed by converting inputted signals of pictures into signals of display formats of picture output devices, which can be applied to all the picture output devices such as a CRT, a liquid crystal display device, a plasma display panel and the like. Therefore, this is a method that is extremely effective in dealing with diversification of input picture sources or picture output devices predicted in the future. According to the method, various signal processing such as conversion of frame rate, compression and expansion of picture size and the like must be performed for format conversion.
For example, when a television signal of PAL system is converted into a television signal of NTSC system and displayed by a CRT or a liquid crystal display device, signal processing such as conversion of frame rate, conversion of number of scanning lines, conversion from interlace scanning into progressive scanning, conversion of aspect ratio or the like, compression and expansion, synchronizing and the like are performed independently each other. Further, memories having a comparatively large capacity such as a line memory, a frame memory are used in many of these signal processing operations. Accordingly, conventionally, a number of memories are needed in a total of signal processing and device cost is increased by using many memories. Further, a variety of input and output interfaces are needed between signal processing and therefore, processing for matching interfaces are often needed, which amounts to an increase in device cost.
Further, in each of signal processing, picture quality is slightly deteriorated, which is caused by, for example, quantization error by AD/DA conversion, band restriction by subjecting signals to a filter or the like. Such a picture quality deterioration is accumulated at each signal processing and the picture quality deterioration cannot be disregarded.